staging: vt6656: rxtx move vnt_usb_send_context into tx structure.

Replacing struct vnt_private.

Where struct vnt_private is needed pointer to priv is added.

This allows to move tx signaling into vnt_usb_send_context.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>